Fuel injection valve

ABSTRACT

A fuel injection valve for a fuel injection system of an internal combustion engines includes a valve closing body cooperating with a valve seat body to form a sealing seat, and a piezoelectric actuator for actuating the valve closing body. The piezoelectric actuator includes piezo layers and one or more temperature compensation layers. The temperature compensation layers have a temperature expansion coefficient having an operational sign opposite the sign of the temperature expansion coefficient of the piezo layers.

FIELD OF THE INVENTION

The present invention concerns fuel injection valves.

BACKGROUND INFORMATION

German published Patent Application No. 195 38 791 concerns a fuelinjection valve for fuel injection systems for internal combustionengines in which the valve closing body is actuated by a piezoelectricactuator. The piezoelectric actuator has a plurality of piezo layersmade of a piezoelectric material. Electrodes are arranged between thepiezo layers so that an electrical voltage can be applied to the piezolayers, causing the piezoelectric actuator, used for actuating the valveclosing body, to expand.

A problem with using piezoelectric actuators is believed to be thermalexpansion. Piezoelectric materials, unlike materials such as steel orplastic, have a negative temperature expansion coefficient. Therefore,the piezoelectric actuator contracts with increasing temperature, whilethe surrounding housing expands. The different temperature expansioncoefficients of the piezoelectric actuator and the housing result in atemperature-dependent valve lift if not compensated using appropriatemeasures.

For temperature compensation, German Published Patent Application No.195 38 791 apparently proposes that the valve housing be designed as twoparts made of two different materials. For example, it is proposed thatone housing part be made of steel and the other housing part be made ofInvar. By an appropriate selection of the length of the first housingpart made of steel and of the second housing part made of Invar, theoverall thermal expansion of the housing should be matched to thethermal expansion of the piezoelectric actuator and thus thepiezoelectric actuator and the housing surrounding the piezoelectricactuator expand and contract in the same manner.

It is believed that a disadvantage of this measure is the cost ofmanufacturing the valve housing and the relatively high cost of thematerial of the second housing part, which is preferably made of Invar.Furthermore, it must be taken into consideration that the valve housingand the actuator may be of different temperatures. Thus thepiezoelectric actuator may heat up due to its heat losses, inparticular, when the fuel injection valve is frequently actuated, andits temperature is only slowly transferred to the valve housing. On theother hand, the temperature of the valve housing is influenced by theheat transferred from the internal combustion engine on which the fuelinjection valve is mounted. This type of temperature compensation istherefore not believed to be satisfactory.

German Patent No. 195 19 192 purportedly concerns a hydraulic lifttransformer arranged between the piezoelectric actuator and the valveneedle that actuates the valve closing body. Temperature compensationresults from the fact that the lift transformer only responds to therelatively quick movement resulting in the intended opening of the fuelinjection valve, whereas a relativity slow, temperature-dependentexpansion or contraction of the piezoelectric actuator may cause thehydraulic fluid to leak out via guide gaps. It is believed that adisadvantage of this design is, however, the relatively high cost of thehydraulic lift transformer.

Other temperature compensation methods include forced tempering of thepiezoelectric actuator using a liquid or gaseous medium, which is heldat a constant temperature in a closed circuit, or a series arrangementof piezoelectric actuators with a temperature-compensating piece, whichis arranged between the piezoelectric actuator and a valve needleactuating the valve closing body, for example. While the first methodmay be relatively costly, the use of a compensating piece arranged inseries is believed to have the disadvantage that the piezoelectricactuator and the compensating piece, as mentioned before, are notnecessarily subjected to the same temperature or the same temperaturevariation; therefore, temperature compensation is relatively inaccurate.

SUMMARY OF THE INVENTION

The fuel injection valve according to an exemplary embodiment of thepresent invention is believed to have the advantage that thepiezoelectric actuator of the fuel injection valve has considerablyimproved temperature compensation. According to an exemplary embodimentof the present invention, one or more temperature compensation layershaving a temperature expansion coefficient with opposite signs withrespect to the temperature expansion coefficient of the piezo layers areprovided directly in the piezoelectric actuator. Through an appropriateselection of the number and thickness of the temperature compensationlayers, accurate temperature compensation can be achieved.

By embedding the temperature compensation layers in the piezo layers ofthe piezoelectric actuator, it is at least better ensured that thetemperature compensation layers are subjected to the same temperatureand the same temperature variation as the piezo layers of the actuator.In particular, a large contact surface exists between the piezo layersand temperature compensation layers, so that the temperature of thetemperature compensation layers and that of the piezo layers are quicklyequalized. This is important because the heat loss of the piezoelectricactuator can be subjected to considerable fluctuation when the actuationfrequency of the fuel injection valve varies as a result of a variationin the internal combustion engine speed. Due to the large contactsurface between the temperature compensating layers and the piezo layersand the proximity of the temperature compensating layers to the piezolayers, temperature compensation by the temperature compensation layerscan quickly follow these fluctuations. In addition, a change in thetemperature of the actuator due to fluctuating amounts of heattransferred from the internal combustion engine can be quicklycompensated by using the method according to the present invention.Expensive forced tempering of the piezoelectric actuator is notnecessary.

In a particularly advantageous manner, the temperature compensationlayers can be used simultaneously as electrodes for activating the piezolayers if the temperature compensation layers are made of a metallicmaterial.

Thus, the piezoelectric actuator is temperature compensated to a highdegree. However, the valve housing surrounding the actuator, which isusually made of metal or plastic, can still be subjected to thermalexpansion resulting in a temperature-dependent position shift of thevalve seat body with respect to the valve closing body connected to theactuator. In order to avoid this, an equalizing sleeve made of a ceramicmaterial is advantageously provided, which either surrounds thepiezoelectric actuator or is itself surrounded by the piezoelectricactuator. The piezoelectric actuator is either in contact with the valvehousing via the equalizing sleeve or actuates the valve closing body viathe equalizing sleeve and, optionally, a valve needle. If the equalizingsleeve has the same axial length as the piezoelectric actuator, thetemperature of the valve housing has no effect on the axial position ofthe valve closing body with respect to the axial position of the valveseat body, i.e., temperature compensation of the valve housing isachieved.

According to an exemplary embodiment, a first end of the piezoelectricactuator is connected to the valve closing body via a valve needle and afirst end of the equalizing sleeve is in contact with the valve housing.A connecting element, which may be plate-shaped for example, is held incontact with the second end of the equalizing sleeve and the second endof the piezoelectric actuator by a spring. According to anotherexemplary embodiment design, the first end of the piezoelectric actuatoris in contact with the valve housing, and the first end of theequalizing sleeve is connected to the valve closing body via a valveneedle. A plate-shaped connecting element is held in contact with thesecond end of the equalizing sleeve and the second end of thepiezoelectric actuator by a spring also in this case.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a section through a fuel injection valve according to anexemplary embodiment of the present invention.

FIG. 2 shows detail II in FIG. 1 in a detailed sectional view.

FIG. 3 shows detail II in FIG. 1 in a detailed sectional view accordingto a variant of the exemplary embodiment of FIG. 2.

FIG. 4 shows a section through a fuel injection valve according toanother exemplary embodiment of the present invention.

DETAILED DESCRIPTION

A section of an injection valve according to an exemplary embodiment ofthe present invention is shown in FIG. 1. Fuel injection valve 1 is usedto inject fuel in particular into an externally ignitedcompressed-mixture internal combustion engine.

Fuel injection valve 1 has a valve closing body 2 designed in one piecewith valve needle 3 and forms a sealing seat together with a valve seatbody 4. The embodiment of fuel injection valve 1 shown in FIG. 1 is afuel injection valve 1 opening outward. A valve seat surface 5 istherefore arranged on the outside of valve seat body 4.

Valve seat body 4 is inserted in an axial longitudinal bore 6 of a valvehousing 7 and sealingly connected to valve housing 7 through welding,for example. Fuel enters via a fuel inlet opening 8 in valve housing 7and goes to the sealing seat formed by valve closing body 2 and valveseat body 4 via a spring support space 9. A restoring spring 10 arrangedbetween valve seat body 4 and a flange 11 of valve needle 3 is arrangedin spring support space 9 formed by axial longitudinal bore 6 of valvehousing 7. Restoring spring 10 transmits a restoring force to valveneedle 3 in the closing direction of fuel injection valve 1.

Valve needle 3 and valve closing body 2 are actuated via a piezoelectricactuator 12 whose first end 13 is in flush contact with end face 14 offlange 11 of valve needle 3. When piezoelectric actuator 12 iselectrically excited, it expands in its axial longitudinal direction anddisplaces valve needle 3 and valve closing body 2 designed in one piecewith valve needle 3 downward in FIG. 1, so that fuel injection valve 1opens. After the electrical excitation voltage is turned off,piezoelectric actuator 12 contracts again, so that valve closing body 2is moved back into its closing position by restoring spring 10.

A feature according to an exemplary embodiment of the present inventionis the layered design of piezoelectric actuator 12. An exemplaryembodiment of the layered structure of piezoelectric actuator 12 isshown enlarged in FIG. 2.

Piezoelectric actuator 12 has a plurality of stacked piezo layers 21made of a piezoelectric material. Electrodes are applied on piezo layers21 such as, for example, by sputtering or vapor deposition, so that anelectric voltage can be applied to piezo layers 21 resulting in anelectrical field being formed in piezo layers 21 in the direction oflongitudinal axis 22 of fuel injection valve 1, causing piezoelectricactuator 12 to expand.

The expansion and contraction of piezo layers 21 depend not only on theelectrical field intensity applied, but also, to a considerable degree,on the temperature. Unlike usual materials, piezoelectric substanceshave a negative thermal expansion coefficient (α<0), which means thatpiezoelectric materials contract with increasing temperature. In orderto prevent an unintended valve motion caused by temperaturefluctuations, this temperature-dependent expansion of piezo layers 21must be compensated. Therefore, according to an exemplary embodiment ofthe present invention, at least one, or a plurality of temperaturecompensation layers 20 are arranged between piezo layers 21. Temperaturecompensation layers 20 have a temperature expansion coefficient whoseoperational sign is opposite to that of the temperature expansioncoefficient of piezo layers 21, which means that temperaturecompensation layers 20 are made of a material with a positivetemperature expansion coefficient (α>0), while piezo layers 21, have anegative temperature expansion coefficient (α<0). By selecting theappropriate number and thickness of temperature compensation layers 20,the sum of contractions or expansions of all temperature compensationlayers 20 corresponds in absolute value to the sum of expansions orcontractions of all piezo layers 21, but with the opposite sign.Effective temperature compensation is achieved in this manner.

In the exemplary embodiment illustrated in FIG. 2, a piezo layer 21 anda temperature compensation layer 20 are alternatingly sandwiched in apiezoelectric actuator 12. FIG. 3 shows, as an enlargement of detail IIin FIG. 1, a piezoelectric actuator 12 having an alternatively layeredstructure, in which a temperature compensation layer 20 is arrangedbetween a plurality of piezo layers 21.

A material having a high positive temperature expansion coefficient suchas aluminum, copper, or a suitable plastic is well-suited fortemperature compensation layers 20; materials having a good thermalconductivity and a low heat capacity, so that the temperature oftemperature compensation layer 20 is quickly equalized to thetemperature of piezo layers 21, are also advantageous.

If temperature compensation layers 20 are made of a metallic material,temperature compensation layers 20 may advantageously also be used aselectrodes for piezo layers 21.

Since temperature compensation layers 20 are arranged in close proximityto piezo layers 21, rapid equalization of the temperature of temperaturecompensation layers 20 to the temperature of piezo layers 21 is ensured,so that temperature compensation is not subject to any considerabledelay.

Through the measures described according to the exemplary embodiment ofthe present invention, effective temperature compensation ofpiezoelectric actuators 12 is achieved, so that the resultingtemperature expansion coefficient of piezoelectric actuator 12 is atleast approximately equal to zero. However, if piezoelectric actuator 12is in direct contact with a solid component of valve housing 7,unintended relative displacement of valve seat body 4 with respect tovalve closing body 2 may occur, which may result in unintended valveopening due to the temperature expansion or contraction of the areas ofvalve housing 7 surrounding actuator 12. Therefore it is proposedaccording to the present invention that the thermal expansion of valvehousing 7 be also compensated. For this purpose, an equalizing sleeve 23surrounding piezoelectric actuator 12 is provided. One end 24 ofequalizing sleeve 23 is in contact with first step 25 of valve housing7. First end 13 of piezoelectric actuator 12 acts via valve needle 3, asdescribed above, upon valve closing body 2. Second end 26 of equalizingsleeve 23, opposite first end 24, and second end 27 of piezoelectricactuator 12, opposite first end 13 are connected via a connectingelement 28 which has a plate-shaped design in the exemplary embodiment.Connecting element 28 is movable in the axial direction in valve housing7 and is held in contact both with second end 26 of equalizing sleeve 23and second end 27 of piezoelectric actuator 12 by spring 29 designed inthe present embodiment as a flat spring. Valve housing 7 is terminatedby an end plate 30, which is in contact with spring 29 and which may beconnected to main body 31 of valve housing 7, for example, by welding.

Equalizing sleeve 23 has the same axial length as piezoelectric actuator12 and is made of a material having an extremely low temperatureexpansion coefficient, preferably a ceramic material or a glassmaterial. Since piezoelectric actuator 12, as described above, istemperature compensated, both equalizing sleeve 23 and piezoelectricactuator 12 are subject to virtually no temperature-dependentlongitudinal expansion. Connecting element 28 is therefore always in thesame axial position regardless of the operating temperature of fuelinjection valve 1 with respect to step 25 of valve housing 7, andregardless of a possible temperature-dependent longitudinal expansion towhich the areas of valve housing 7 surrounding equalizing sleeve 23 andpiezoelectric actuator 12 are subjected. Therefore,temperature-dependent expansion of these areas of valve housing 7 causesno axial displacement of valve seat body 7 with respect to valve closingbody 2. If valve needle 3 and a section of valve housing 7 between step25 and valve seat body 4 are made of the same material, a change intemperature in this area also causes no relative change in the positionof valve closing body 2 with respect to valve seat body 4, so that fuelinjection valve 1 as a whole is effectively temperature compensated.

FIG. 4 shows another embodiment of fuel injection valve 1 accordinganother exemplary embodiment of the present invention. In the exemplaryembodiment shown in FIG. 4, temperature compensation is implemented in afuel injection valve 1 opening inward. In order to facilitateidentification, elements described previously are provided with the samereference symbols, so that a redundant description is unnecessary.

In the exemplary embodiment illustrated in FIG. 4, piezoelectricactuator 12 has a sleeve shape. It has, however, the same layeredstructure as shown in FIGS. 2 and 3, i.e., temperature compensationlayers 20 are arranged between piezo layers 21, so that piezoelectricactuator 12 is temperature compensated. The effective temperatureexpansion coefficient of actuator 12 is therefore essentially equal tozero. In the exemplary embodiment illustrated in FIG. 4, an equalizersleeve 23 made of a ceramic material and surrounded by piezoelectricactuator 12 may be provided. Fuel inlet opening 8 is formed at a fuelinlet nozzle 40 at the end of fuel injection valve 1 opposite valve seatbody 4. Fuel is supplied to the sealing seat via an axial bore 41 infuel inlet nozzle 40, a cutout 42 in plate-shaped connecting element 28,an axial longitudinal cutout 43 in equalizing sleeve 23, through bores44 in flange 11 of valve needle 3, and spring support space 9. Thepulling spring 45 is provided in spring support space 9.

Furthermore, a connector plug 46 used for electrical contacting ofpiezoelectric actuator 12 is illustrated in FIG. 4. Connector plug 46may be designed as an injection molded plastic part, for example.

When piezoelectric actuator 12 is electrically actuated, its first end13 is in contact with step 25 of valve housing 7 and displacesplate-shaped connecting element 28 in FIG. 4 upward against spring 29.Flange 11 of valve needle 3 is held in contact with first end 24 ofequalizing sleeve 23 by pulling spring 45. At the same time, second end26 of equalizing sleeve 23 is permanently held in contact withplate-shaped connecting element 28. Therefore, the expansion ofpiezoelectric actuator 12 causes valve closing body 2 to lift and fuelinjection valve 1 to thereby open. It is essential that the elasticforce of spring 29 be greater than the elastic force of pulling spring45. When the electrical excitation voltage is turned off, piezoelectricactuator 12 contracts again so that spring 29 again brings valve closingbody 2 in contact with valve seat body 4 via plate-shaped connectingelement 28, equalizing sleeve 23, and valve needle 3 and thus closesfuel injection valve 1.

Since equalizing sleeve 23 has the same axial length as piezoelectricactuator 12 and both piezoelectric actuator 12 and equalizing sleeve 23have an extremely low temperature expansion coefficient, valve lift isalmost temperature-independent. In particular, the area of valve housing7 surrounding piezoelectric actuator 12 and equalizing sleeve 23 have noinfluence on the valve lift, since its thermal expansion is compensatedby spring 29.

A conducting compound can be applied between actuator 12 and equalizingsleeve 23 either in the exemplary embodiment of FIG. 1 or in theexemplary embodiment of FIG. 4 for improved heat capacity betweenequalizing sleeve 23 and actuator 12.

Instead of pulling spring 45, the flush contact between flange 11 ofvalve needle 3 with first end 24 of equalizing sleeve 23 and the flushcontact with second end 26 of equalizing sleeve 23 with plate-shapedconnecting element 28 can also be implemented by gluing or pressing, forexample.

Since fuel flows through the center of fuel injection valve 1 accordingto the exemplary embodiment illustrated in FIG. 4, rotation-symmetriccomponents can be used, which allows inexpensive manufacturing. Fuelinjection valve 1, with fuel flowing through its center, requires nolateral fuel inlet opening 8. Therefore installation on an internalcombustion engine using normal hydraulic connecting methods issimplified. Due to the fact that no parts subject to wear are used, along-lasting fuel injection valve 1 results according to the exemplaryembodiments of the present invention.

What is claimed is:
 1. A fuel injection valve for a fuel injectionsystem of an internal combustion engine, the fuel injection valvecomprising: a valve seat body; a valve closing body cooperating with thevalve seat body to form a sealing seat; a piezoelectric actuator foractuating the valve closing body, wherein the piezoelectric actuatorincludes a plurality of piezo layers made of a piezoelectric materialhaving a negative temperature expansion coefficient, and at least onetemperature compensation layer having a positive temperature expansioncoefficient, the piezoelectric actuator having a first end facing thevalve seat body and a second end distal to the valve seat body; a valvehousing; and an equalizing sleeve made of a material having a lowtemperature expansion coefficient, wherein the equalizing sleevedetermines an axial position of the piezoelectric actuator in the valvehousing, and wherein the equalizing sleeve has a first end having anaxial position equivalent to the first end of the piezoelectricactuator, and a second end having an axial position equivalent to thesecond end of the piezoelectric actuator.
 2. The fuel injection valve ofclaim 1, wherein a thickness of the at least one temperaturecompensation layer provides that the piezoelectric actuator exhibits atleast one of a reduced length change and an essentially zero lengthchange as a function of a temperature change.
 3. The fuel injectionvalve of claim 1, wherein the plurality of the piezo layers and the atleast one temperature compensation layer are alternatingly sandwiched inthe piezoelectric actuator.
 4. The fuel injection valve of claim 1,wherein the at least one temperature compensation layer is arrangedbetween the plurality of the piezo layers in the piezoelectric actuator.5. The fuel injection valve of claim 1, wherein the at least onetemperature compensation layer is made of one of copper, aluminum and asuitable plastic.
 6. The fuel injection valve of claim 1, wherein the atleast one temperature compensation layer is made of a metallic materialand is used at a same time as electrodes for the plurality of the piezolayers.
 7. The fuel injection valve of claim 1, further comprising: avalve needle; and a connecting element; wherein: the first end of thepiezoelectric actuator is connected to the valve closing body via thevalve needle; the first end of the equalizing sleeve contacts the valvehousing; and the connecting element contacts the second end of thepiezoelectric actuator and the second end of the equalizing sleeve. 8.The fuel injection valve of claim 1, wherein the equalizing sleeve ismade of a ceramic material.
 9. A fuel injection valve for a fuelinjection system of an internal combustion engine, the fuel injectionvalve comprising: a valve seat body; a valve closing body cooperatingwith the valve seat body to form a sealing seat; a piezoelectricactuator for actuating the valve closing body, wherein the piezoelectricactuator includes a plurality of piezo layers made of a piezoelectricmaterial having a negative temperature expansion coefficient, and atleast one temperature compensation layer having a positive temperatureexpansion coefficient, the piezoelectric actuator having a first endfacing the valve seat body and a second end distal to the valve seatbody; a valve housing; and an equalizing sleeve made of a materialhaving a low temperature expansion coefficient, wherein the equalizingsleeve determines an axial position of the piezoelectric actuator in thevalve housing, and wherein the equalizing sleeve has a first end havingan axial position equivalent to the first end of the piezoelectricactuator, and a second end having an axial position equivalent to thesecond end of the piezoelectric actuator, wherein the equalizing sleeveconnects the piezoelectric actuator to the valve closing body, thepiezoelectric actuator being formed as a sleeve that surrounds theequalizing sleeve.
 10. The fuel injection valve of claim 9, furthercomprising: a valve needle; a spring; and a connecting element; wherein:the first end of the piezoelectric actuator contacts the valve housing;the first end of the equalizing sleeve connects to the valve closingbody via the valve needle; and the connecting element is held by thespring in contact with the second end of the piezoelectric actuator andthe second end of the equalizing sleeve.
 11. The fuel injection valve ofclaim 9, wherein the equalizing sleeve is arranged so that fuel injectedby the fuel injection valve flows through the equalizing sleeve.